With development of broadband network, mobile communications are not only limited to traditional voice communication. Multimedia service, which combines a plurality of media types, such as audio, video, photo and text, etc., will be developed gradually, and through combination with Presence (presence service), SMS (short message service), WEB browsing, location information, PUSH (push service), file sharing and other data services, it can satisfy various requests of users, e.g.:
message services: instant message and chat room, multimedia short message;
video services: entertainment, multimedia information, daily communication;
electronic commerce: product catalog, search engine, cart, order form management, payment;
game: single game, group game;
location service: searching for people, guiding, alarming;
personal assistant: address book, calendar, bookmark management, file storage, event reminder, E-mail.
Under promotion of various applications, 3GPP (3rd Generation Partnership Project), 3GPP2 (3rd Generation Partnership Project 2) and other standard organizations all successively launch an IMS (IP Multimedia Subsystem) architecture, with a purpose to implement various multimedia applications using a standard open structure in a mobile network and provide more choices and wonderful feelings.
In 3GPP Release 5 (R5) phase, an IMS is introduced, which is added to a packet domain network and includes such function entities as CSCF (Call Session Control Function), MGCF (Media Gateway Control Function), MRF (Multimedia Resource Function) and HSS (Home Subscriber Server), etc. The CSCF can also be divided into three logic entities, which are S-CSCF (Service CSCF), P-CSCF (Proxy CSCF) and I-CSCF (Inquiry CSCF), wherein S-CSCF, as a service switching center of IMS, executes session control, maintains session state, manages user information, and generates charging information, etc.; P-CSCF, as an access point for a terminal user to access the IMS, finishes subscriber register, and is responsible for QoS control and security management etc.; I-CSCF is responsible for intercommunications between IMS domains, manages S-CSCF allocation, hides network topology structure and configuration from the outside, and generates charging data, etc. MGCF controls gateways and implements intercommunication between IMS network and other networks; MRF provides media resources, such as receiving/broadcasting voices, coding/decoding, establishing multimedia conference bridge; HSS is a user database, which stores subscription data and configuration information of IMS users, etc.
Because IMS network structure has no relation with a lower-layer bearer network, the IMS network defined by 3GPP can be applied to other packet networks besides the packet domain network defined by 3GPP, such as the packet network defined by 3GPP2, WLAN network, and NGN network, etc., independent of user terminal type and access network type. Therefore here IMS is not limited to be used in networks and applications related to 3GPP, but can be used in services and applications of other types of access networks and bearer networks.
Session Initiation Protocol (SIP): SIP is an IP phone signaling protocol proposed by IETF (Internet Engineering Task Force). As is implicated by its name, SIP is used to initiate a session, can control establishment and termination of a multimedia session joined by many participants, and can dynamically adjust and modify session attributes, such as session bandwidth request, transmitted media types (voice, video and text, etc.), media coding/decoding formats, support for multicast and unicast, etc. In an IMS, SIP protocol is used as a signaling control protocol of an IP multimedia session.
A new framework of AAA—Diameter protocol:
AAA, i.e. Authentication, Authorization and Accounting, up to today, is always a foundation based upon which network carriers run and manage networks. With development of AAA, a new framework Diameter technology has come into being.
Diameter protocol suite includes a base protocol (Diameter Base Protocol) and various application protocols. The base protocol provides the lowest requirements of the AAA protocol for functions that must be achieved by all of Diameter network nodes, including negotiation of ability between the nodes, receiving and forwarding of Diameter messages and real time transmission of charging information, etc. The application protocols adequately utilize a message transmission mechanism provided by the base protocol and standardize functions and special message contents of corresponding nodes to implement AAA of application services.
In the IMS, Diameter protocol is used to transmit corresponding information on a Cx interface between HSS and I-CSCF and between HSS and S-CSCF.
Home Subscriber Server (HSS):
HSS, the most important database for each user, stores all information related to subscription and is used to support processes on a call or a session by each network entity, specifically including: user ID, number and addressing information, user security information, user location information and user profile information, etc. Home network can have one or several HSSs depending on the number of mobile subscribers, capacity of network devices and detailed networking situations. There are interfaces between HSS and several network entities, in which an interface between HSS and I-CSCF or between HSS and S-CSCF is a Cx interface.
In future multimedia applications, user equipments will be capable of supporting several media types, such as audio, video, text and image, etc., and each media type can support more than one coding/decoding format. Accordingly, user equipments may need to have various built-in or external devices. For a mobile phone, since its smaller size, Plug and Play devices are used more often, such as video camera, potable mobile store device, MP3, external keyboard, etc. Presence or absence of each of these devices means whether a terminal user can use a certain multimedia application, for example, the presence of video camera means that the user can initiate a video call. Even if the device is not a Plug and Play device, it may need to be configured by users to be enabled or disabled; for example, a built-in recoding function, infrared function etc., is enabled through special combination of keys on a keyboard.
Since these devices come into effect immediately once they are used, from the moment they take effect, the capability of the user equipment changes. A method of informing the network of the changed capability of the user equipment in time is needed, so that the network can know the capability of the user equipment immediately, and further determine whether to accept some service requests from the user equipment and whether to accept some service requests from other user equipments when the user equipment is called.
At present, in an IMS network, a negotiation on capability of a UE (user equipment) is implemented through a process of establishing and modifying an SIP session. When a UE (or mobile terminal) initiates to establish an SIP session, an INVITE message is used to bring the capabilities of a calling UE to the network and an opposite end UE. Each network node related to the session and the opposite end UE need to determine whether to accept the session establishment according to their respective support capabilities and support capability of the calling UE, for example, a P-CSCF (including a calling P-CSCF and a called P-CSCF) determines whether to allow establishment of the SIP session initiated by the calling UE or called UE according to a local strategy, and S-CSCF (including a calling S-CSCF and a called S-CSCF) determines whether to allow establishment of the SIP session initiated by the calling UE or called UE according to a local strategy or the subscriber profile downloaded from the HSS, while the called UE determines whether to accept the request of establishing the session according to its own capability. If the capability of the calling UE or called UE has changed before completion of the INVITE session, for example, a PnP device is plugged/unplugged or a built-in function is enabled/disabled etc., the related UE can modify the establishing SIP session by sending an UPDATE message bearing information of the changed capability of the UE and a network node and opposite end UE, after receiving the UPDATE message, will renegotiate the session establishment according to the changed capability of the UE and if the negotiation succeeds, the new capability of the UE is used to perform the session, or if the negotiation fails, the old capability of the UE is still used to establish the session. If the INVITE session has finished, an SIP session has been established successfully and a real service data transmission has been started between the calling UE and called UE or the calling UE and an AS (Application Server), and at this time the capability of the calling UE or called UE changes, for example, a PnP device is inserted or a certain built-in function is enabled to be used in the present service, a RE-INVITE message can be reinitiated, bearing information of the changed capability of the terminal, and the present session is renegotiated according to a re-negotiation process similar to the negotiation process of INVITE. After the re-negotiation succeeds, the new capability of the terminal is used to perform the service and the old negotiation result is deleted, or if the negotiation fails, the old negotiation result is still used to perform the service.
Besides the method of informing the network and opposite end UE of the user equipment capability during the session establishing and modifying process, when each UE establishes contact with the IMS network for the first time, that is, when it initiates an IMS register, the capability information of the user equipment can be encapsulated in a REGISTER message and sent to the network, and is stored in an S-CSCF for determining subsequent processes by the S-CSCF when the S-CSCF receives a request of establishing or modifying a SIP session subsequently.